In the medical and biological fields, including those involving research, clinical testing and processing, fluids are commonly tested or filtered which contain proteinaceous materials. Many of the media used in diagnostic testing or filtration provide adequate performance with respect to retention of materials sought to be retained, such as solid or gelatinous materials. Commonly, such media used for filtering proteinaceous material-containing fluids also provide rapid flow rates when initially placed in service by virtue of low pressure drops across the membranes. Many of these materials, such as cellulose esters, however, exhibit poor hydrolytic stability and tend to decompose slowly when subjected to continuous use and particularly when exposed to conditions of steam sterilization. There is a tendency by some media, particularly cellulose esters such as cellulose acetate and cellulose nitrate, to decompose as a result of prolonged exposure to solvents or biological materials. In addition, some of these materials tend to be brittle and cellulose nitrate is flammable.
Other media, such as polyamides, particularly nylon, exhibit generally good hydrolytic stability, relatively low flammability and desirable physical properties, such as high strength and flexibility. The polyamides, particularly nylon 66, demonstrate high retention of materials sought to be retained, usually resulting from precise manufacturing control of absolute pore ratings. In many applications, polyamide media are employed in the form of membranes which exhibit low pressure drops across the membrane. However, when such applications involve filtration or passage of solutions containing proteinaceous materials, the pressure differentials across the filtration media frequently increase during use because continued contact of such membranes with proteinaceous materials results in the pores of the membrane being plugged and performance thereby being adversely affected. When such membranes are used in filters, this typically means that flow rates are reduced and high increases in pressure drop are encountered. In many instances, the blockage is irreversible and a costly membrane must be discarded. Thus, a membrane which in most respects is quite suitable for the intended purpose is rendered useless by an undesirable adsorption of proteinaceous material. Furthermore, in many instances the proteinaceous material is not a material which is sought to be removed from the fluid and its retention causes unwanted results. In some instances, the retained protein may be unusable and may, therefore, represent a costly loss.